POLICE say a three-year-old Oberon boy left unconscious and critically injured on Sunday afternoon may have been knocked over by his family's dogs and are seeking witnesses to the incident.

The boy, along with his mother and stepfather were walking in the park, known as the soccer fields, on Cunynghame Street at 1pm on Sunday when the incident occurred.

Chifley Local Area Command Crime Manager Detective Inspector Luke Rankin said police were told the boy had been "knocked down and struck his head" after he became tangled in the leads of the two family dogs.

"The dogs [an Alsatian and a husky] were on a lead and they got loose and in some way the leads have tripped the child over," he said of the mother's report to police.

"The child had been rendered unconscious and rushed home from where emergency services were called."

A crime scene was established at the family home, with forensic police officers called in to examine the inside and outside of the home, along with an area in the park following the accident.

Police on Monday removed a number of items from the family property including several boxes of ammunition.